Economic Studies of Carbonation Processes, Turning Feasibility into Reality

Is carbonation a viable approach to climate change mitigation through CO₂ emissions reduction? Can carbonation overcome its well-known drawbacks, energy demand, a large amount of material handling etc? Most of these answers arise from the literature, and indicate that carbonation can be considered as viable CO₂ reduction approach from a technical point of view. Nevertheless, a technically demonstrated process needs to be economical (profitable) to be implemented.

Keys to economic success are becoming more and more evident. Carbonation cannot compete with underground storage and cannot only act as a sequestration technique. Processes should be efficient with both raw flue gas or pure CO₂ streams (sugar cane refineries or fertilizer sources). This way, CO₂ is removed from gaseous streams and is used/stored on site. This can be game changing in areas where underground storage is not an option. On the other hand, value added by-products need to be generated. Besides the potential income from such by-products, reuse of the waste material used as carbonation feedstock is needed to meet sustainability standards.

Such an approach has been triggering research made at INRS since 2012 to develop a direct flue gas carbonation process using waste mining residues. The process first developed under laboratory conditions showed the potential of using carbonic acid alone to leach Mg from heat activated serpentine. Combined with ambient temperature, moderate pressure, and successive recirculation, Mg was extracted in significant quantities with CO₂ removal around 65%. Furthermore, by separating the gas and pulp contacting steps from the carbonate precipitation, very pure hydrated magnesium carbonates are obtained. This high purity results in high potential sales value, and profitability. Later, the demonstration at a “pilot scale” using a flue gas within an operating cement plant confirmed laboratory scale results. Consequently, following the promising results, similar approaches were tested with steel slags and waste concrete.

A common point with all these research projects is the integration of economic evaluations at an early stage. As a result, process development is performed in a close loop with economic viability. The presentation will highlight the economic considerations and evaluation for the different approaches considered at INRS.